Midrash su Deuteronomio 25:15

Rabbi said: Blessings³⁷In the sense of good deeds. bring blessings upon their purveyors; curses³⁸In the sense of evil deeds. bring curses upon their purveyors. Blessings bring blessings upon their purveyors, as it is written: “A whole and just weight shall be [yours]” (Deuteronomy 25:15), and if you do so: “shall be yours” (Deuteronomy 25:15). Curses bring curses upon their purveyors, as it is written: “You shall not have in your purse different weights, large and small” (Deuteronomy 25:13), and if you do so, the Holy One blessed be He said: ‘You sought to use large and small? By your life, that wicked one [who uses corrupt weights] will not manage to possess even something small,’ as it is written: “You shall not have in your purse.” Similarly, “you shall not make with Me [gods of silver and gods of gold]” (Exodus 20:20). The Holy One blessed be He said: ‘You sought to make for Me “gods of silver and gods of gold” – by your life, that wicked one will not manage to make even one of wood,’ as it is written: “You shall not make for yourselves” (Exodus 20:20).

Our Rabbis were taught: Whence is it deduced that one must not make [the measure] level where the custom is to heap it; and heap the measure where the custom is to have it level? The passage reads (Deut. 25, 15) A perfect and just measure shalt thou have. And whence is it deduced that where the custom is to heap the measure, if one say: 'I will make it level and diminish the price,' or in places where the custom is to make it level, 'I will heap and increase the price,' that he must not be listened to? The passage reads therefore: A perfect and just measure shalt thou have," (i.e., just refers not to make any charge). R. Juda of Sura said (Ib., ib. 14) Thou shalt not have in thy house. Why? Because [you practice] diverse measures. Thou shalt not have in thy bag. Why? Because [you practice] diverse weights. But when you will practice a perfect and just weight, then shalt thou have (prosperity).